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Shriek, sob, swoon: What's behind Bieber fever?

TODAY

A Justin Bieber fan gets hysterical at the concert.

They’d been camping on the streets of New York City for three days -- throngs of teen and tween girls, who had gone without showers (except for the ones that fell from the sky) in the hopes of getting a front row glimpse of their favorite teenage heartthrob.

And when everyone’s imaginary “Boyfriend” Justin Bieber took the stage this morning to play a mini-concert for TODAY, these super-fans did what teen groupies have done for eternity: they screamed, they cried, they quivered. 

So what's behind all the shrieking and sobbing, the shaking and swooning? Is there a physiological explanation for this fan-demonium or is it simply tween and teen girls gone wild?

"It's basically a group response set off by emotions and hormones," says Dr. Sarah Pitts, a specialist in adolescent medicine at Boston Children's Hospital.

TODAY

The crowd surrounds The Biebs.

A lot has to do with what's happening in the heads of tweens and teens. In those early adolescent years from 10 to 14, kids are searching for new people to love outside of their family and they might glom on to a celebrity crush, suggests Pitts.

In addition, being around groups of young people may also make this behavior more "contagious" during a phase when peer pressure rules. For the 15- and 16-year old Bieber fans in the audience, there's also the growing interest in forming relationships and sexual attraction that fuels the emotional excitement of seeing your teen idol.

"The teen brain is still significantly changing and not yet in its final form," points out Pitts. "And that affects how teens respond to the world around them."

Young girls are especially prone to getting emotional and when they get excited, they cry "happy tears."

"I don't know that there's a scientific basis for that," admits Pitts. "It comes down to the chemistry in our brains and nerves."

As for keeling over, Pitts says fainting is really common in teens, more so in females.

If a young Bieber fan has been standing outside for hours, and they're sleep deprived and very excited, and perhaps also hungry and cold, then passing out is a possibility. It's more of an emotional faint, in which falling over is actually protective allowing blood to quickly shunt back to the brain.

Of course, this generation is not the first to weep, screech, and faint at its teenage heartthrobs. These behaviors go way back. If it wasn't the Biebs who was bringing on the waterworks and hysteria, it was the Jonas Brothers, or ‘N Sync; the Jackson 5, the Beatles or Elvis.

So why don't young boys scream and swoon at a Miley Cyrus or Selena Gomez concert? "Boy's brains and hormones are wired differently," says Pitts. And while it's culturally OK for girls to cry, that's not the behavioral norm for guys.

Then again, maybe it's just that chicks are the bigger Bieber "believers." 

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